Rechargeable batteries, i.e., secondary batteries, have been widely used to provide electrical power for driving battery powered electronic appliances. Battery powered electronic appliances may include, by way of example, portable radio cassette players, portable computers, camcorders, digital cameras, cellular telephones, PDAs and other devices. Alkaline batteries for such appliances, such as nickel cadmium (Ni—Cd) or nickel metal hydride (Ni—MH) batteries, are well known. Recently, lithium ion (Li-ion) batteries with an organic electrolytic cell have gained popularity in high-end portable electronic devices because they exhibit high energy density, low temperature characteristics, and stable storage capability.
Rechargeable batteries require an electronic charger for recharging depleted batteries. A charger may be configured as internal charger circuit incorporated into the battery-powered appliance. An internal charger typically begins charging the battery whenever the device is powered by an alternating current (AC) source, and allows discharge of the battery when the AC source is removed.
Typically, internal charging circuits are configured to include protection against an overcurrent condition at the battery. For example, when an AC source is applied to the circuit and the battery is discharging, the instantaneous current through the battery can exceed safe or desired levels. A battery including an electrolytic cell can explode in an overcurrent condition, while other batteries may be seriously damaged. Also, an internal charging circuit may be configured to prevent cross-conduction between batteries in a multiple battery system. Cross-conduction between batteries can occur if the charging circuit allows two or more batteries to simultaneously conduct, and can result in inefficient or ineffective power transfer to system components.
In view of these considerations, charging circuit topologies typically require numerous components, and are thus costly to manufacture. However, known battery charging circuit topologies, especially those adapted for use with multiple batteries, achieve battery charging/discharging using redundant circuit components. This adds to the cost and complexity of the system, and creates inefficiency in power transfer to system components.
Thus, there is a need for a battery charging circuit topology allowing low component count and efficient power transfer in battery powered electronic appliances.